A vertically adjustable door assembly for use in a modular wall assembly includes a door opening defined by first and second door jamb assemblies which are adapted to receive vertical slider members in a channel disposed along a length of the door jamb assemblies. The slider members are vertically adjustable within the channels and include hinge mechanism such that either door jamb assembly can support a door member therefrom. Another aspect of the invention includes a vertically adjustable header assembly providing an aesthetically pleasing uniform appearance between the door assembly and the modular wall assembly.